The present invention relates to phonograph cartridges and in particular to an improved stylus arm for such cartridges and a method for manufacturing the same.
In the typical phonograph cartridge a record engaging stylus is used to trace the undulations of a record's grooves and to transmit the same to a magnetic or electro-magnetic circuit so as to cause changes in the circuit and hence produce an output electrical signal which, after suitable amplification, reproduces the recorded information. The stylus is commonly mounted to one end of an arm upon which a permanent magnet or magnetic member is also mounted for movement within a magnetic circuit. As the stylus moves the movement is transmitted through the arm to the magnetic element which results in some change in the flux pattern of the magnetic circuit and hence the desired output signal being induced.
It can thus be seen that the arm which forms the connection between the stylus and magnetic element is critical to insure that the information recorded is properly played back. While it would appear that a stiff arm is desirable to insure that movement of the stylus is accurately transmitted to the magnetic element, an overly stiff arm could resonate at frequencies within the cartridge operating range. Such resonance could cause the stylus to cut into the walls of the record groove thereby damaging the record. On the other hand, if the arm is not sufficiently stiff, the movement of the stylus would not be accurately transmitted to the magnetic element.
The critical parameter in the design of stylus arms has been found to be the stiffness/weight ratio. The lower the ratio the more likely the tube is to resonate and hence cause possible record damage. For this reason, it has been customary for the stylus arm to be in the form of a hollow tube to maximize stiffness for a given weight. Aluminum is the preferred material for the arm tube because of the relative ease with which it can be worked into a desired shaped.
With the above in mind, it is the principal object of the present invention to provide an improved stylus arm wherein the stiffness/weight ratio may be controlled as required.
A further object is to provide such an arm which may be formed and worked utilizing conventional equipment.
A still further object is to provide such an arm wherein the stiffness may be increased without any appreciable change in the weight of the arm for a given size, material and shape.
Still other objects and advantages will be apparent from the following description of the invention.